This invention relates to sonar apparatus.
For many sonar applications it is desirable that sonar transducers should be positioned between the sea bed and a surface vessel carrying out a sonar survey. This is normally achieved by means of a sonar transducer transmitter/receiver array which is carried by an underwater vessel towed by the surface vessel carrying out the survey. Sonar transducers of this kind are usually described as towed arrays or towed bodies and comprise a number of transducer elements, signals from which are conveyed to the surface vessel via a towing cable. A relatively large number of elements are normally used to form the array whereby beam forming utilising signal processing techniques is facilitated.
It will be appreciated that such techniques require a large number of electrical conductors to convey signals relating to each transducer element to the surface vessel or alternatively a complex multiplexing of the signals from the elements is required prior to transmission to the surface vessel. In addition complex processing techniques are required to resolve the received signals
With sonar systems as previously described considerable difficulty in resolving the received signals occurs if there is displacement of the towed vessel or body other than in the towing direction e.g. as a result of partial rolling movement or as a result of yaw. Attempts have been made to reduce such movements of the towed vessel by way of aerodynamic shaping or steering but with only limited effect. In addition attempts have been made to compensate for such movement by sensing displacement of the towed vessel from a required orientation and by compensating the processed signals in response thereto. This again requires complex processing and requires further information to be relayed to the surface vessel for processing.